Field of the Invention
The present invention relates to a hard-material threaded connection, to a method for forming a threaded connection between hard material and a component having higher elasticity and to a structural part having a hard material and possessing a first threaded portion formed in the hard material.
Particularly in the sector of the cutting machining of metallic workpieces, it is known to use tools which have a tool body and an exchangeable cutter, particularly in the form of a cutting head, fastened to the tool body. The cutter is in this case usually manufactured from a hard material and is designed to come into cutting engagement with the workpiece, whereas the tool body is formed from a material having higher elasticity (as compared with the hard material), such as, for example, from a steel, and connects the cutting head to other components of a machine tool. In this case, the tool body or a threaded body connected to the tool body forms a component having higher elasticity, and the cutting head is a structural part which has a hard material.
In the present context, the term “hard material” embraces hard metals, cermets and cutting ceramics. In this case, cutting ceramics are understood to mean ceramics which are used in metal cutting machining, in particular cubic boron nitride and polycrystalline diamond. In the present case, hard metal (also designated as “cemented carbide”) is understood to mean a material in which hard metal carbides are embedded in a metallic matrix (binder). The metal carbides may in this case be formed, in particular, by carbides or composite carbides of the metals of groups IV to VI of the periodic table of elements, in particular, for example, by carbides or composite carbides of the metals W, Ti, Zr, Hf, V, Nb, Ta, Mo and Cr. The metallic matrix may be formed in particular, for example, by Co, Ni and/or Fe. Additions of further hard materials may also be present. Cermet is understood to mean a material in which ceramic particles, which may be formed, in particular, by carbo-oxides, oxides, borides or carbides, are embedded in a metallic matrix. The metallic matrix may in this case have, in particular, cobalt (Co), tungsten (W), molybdenum (Mo), niobium (Nb), titanium (Ti), zirconium (Zr), chromium (Cr) and/or nickel (Ni).
It is known to connect structural parts, which have a hard material or are formed from hard material, via a threaded connection to the component which has higher elasticity. In this case, the hard-material structural part is provided with a first threaded portion which is usually (but not necessarily) formed by an internal thread, and the component having higher elasticity is provided with a matching second threaded portion which is usually formed correspondingly by an external thread. The threaded connection is in this case, particularly with regard to a rotating tool, designed in such a way that it is loaded, upon the use of the tool, in a direction which screws shut the threaded connection somewhat further, so that an undesirable release of the threaded connection by turning loose is not to be feared. The threaded connections which are employed are standard threads, such as, for example, metric ISO threads.
The problem arises, in practice, that a failure of the threaded portion on the hard-material structural part may occur, inter alia, because of the different material properties of the hard material and of the material of the component having higher elasticity. It happens, in particular, that thread flights are stripped or ring-shaped chips or cracks occur in the structural part made from hard material.